Weighted output sensor

ABSTRACT

A sensor comprises a sensing element to generate output signals corresponding to receiving signals received from an object and an evaluation unit coupled to the sensing element and weighting the output signals from the sensing element with at least one switching threshold to generate object detection signals. The evaluation unit includes a key adapted to selectively reset the at least one switching threshold to higher and lower values through differences in activation of the key.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority of the German Patent Application DE10 2007 051 979.8, filed on Oct. 31, 2007, the subject matter of whichis incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a sensor comprising a sensing elementand an evaluation unit, in which the output signals from the sensingelement are weighted with at least one switching threshold forgenerating object detection signals.

Sensors of this type are generally used for detecting objects and can beembodied as optical sensors, ultrasonic sensors and the like.

A sensor of this type is normally provided with a sensing element fordetecting objects. The sensor is furthermore provided with an evaluationunit for evaluating the output signals from the sensing element. In theprocess, the output signals are weighted with the aid of one or severalswitching thresholds, thereby generating an object detection signal,which indicates whether or not an object has been detected, preferablywithin a specified area.

An optical sensor in the form of a light sensor, such as a photoelectricsensor, is one example for such a sensor. This light sensor is providedwith a sensing element that consists of a transmitter for emitting lightrays and a receiver for receiving light rays, which are connected to theevaluation unit and are integrated into a joint housing together withthe evaluation unit.

For detecting an object, the light rays emitted by the transmitter areconducted to the object. These light rays are reflected by the objectand then travel back as receiving light rays to the receiver. The outputsignals from the sensing element are the receiving signals of thereceiver. These signals are weighted with a switching threshold forgenerating a binary object detection signal. The switching thresholddefines a detection distance which, in turn, defines an area ofcoverage. Depending on whether the currently received signal is locatedabove or below the switching threshold, the object detection signalassumes either the switching state “object detected in the detectionrange” or “detection range clear.”

The switching threshold for light sensors of this type is determinedduring a teach-in process. Following the triggering of such a teach-inprocess, e.g. by activating a button on the sensor, an object is placedrelative to the sensor at the detection distance to be set for thesensor. Following this, the object arranged at the detection distance isscanned with the aid of transmitted light rays and is thus detected. Theswitching threshold value is then derived from the receiving signals atthe receiver output, which are recorded in the process. In the simplestcase, the level recorded for the receiving signals is adopted directlyas a switching threshold. Besides the value for the receiving signallevel, an additional value that is stored in the evaluation unit, aso-called functional reserve, is preferably also added and the sumformed in this way is adopted as the switching threshold. The teach-inprocess is thus completed and the sensor operation can start, whereinduring the operating phase for generating the object detection signal,the currently recorded receiving signals are compared to the switchingthreshold. If the switching threshold must be changed, then a newteach-in process must be realized, which requires a considerableexpenditure in time.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a sensorof the aforementioned type, for which a parameter setting can berealized easily, quickly, and with low structural expenditure.

The above and other objects are achieved according to one embodiment ofthe invention wherein there is provided a sensor comprising: a sensingelement to generate output signals corresponding to receiving signalsreceived from an object; and an evaluation unit coupled to the sensingelement and weighting the output signals from the sensing element withat least one switching threshold to generate object detection signals,the evaluation unit including a key adapted to selectively reset the atleast one switching threshold to higher and lower values throughdifferences in activation of the key.

With the sensor according to the invention, switching thresholds can beadjusted as sensor parameters, without requiring a teach-in process. Incontrast to the switching threshold setting via teach-in processes, thesensor parameter setting according to the invention can be realizedeasier and faster.

One essential advantage of the invention is that the same key can beused to reset the switching threshold to higher values as well as lowervalues. In general, all threshold setting operations can be carried outwith the same key, thereby resulting in an extremely low structuralexpenditure for the embodiment of the setting means. The key, which ispreferably arranged on one outside wall of the sensor, furthermore iseasy to operate and handle for the respective operator making theadjustment.

The operation of the key is generally configured such that differentfunctionalities of the parameter setting are triggered in the evaluationunit for the sensor, depending on the length of time during which thekey is activated or depressed.

Different time windows are defined for this in the evaluation unit,wherein these time windows preferably follow each other continuously,without gap. A specific adjustment operation is assigned to each timewindow. A check is then carried out in the evaluation unit to determinewhich time window is associated with the respective length of time fordepressing the key. The function respectively associated with this timewindow is then activated.

It is particularly advantageous if a first and a second time window aredefined, wherein the first time window is assigned the setting function“increase switching threshold” and the second time window the settingfunction “reduce switching threshold.” Once an operator activates,meaning depresses, the key then the evaluation unit evaluates the lengthof time during which the key is activated and the switching threshold iseither increased or reduced, depending on the time window into which thelength of activation falls.

The second time window in particular is preferably associated withlonger times than the first time window. Thus, corresponding to thesubjective finding of the operator, the switching threshold is increasedif the key is depressed for a longer period and the switching thresholdis decreased if the key is depressed for a shorter period.

The switching threshold is advantageously changed by the same amounteach time the key is activated. That is to say, the step distance forchanging the switching threshold is identical for the increase as wellas for the reduction of the switching threshold. By depressing the keyseveral times, the switching threshold can thus be increased or reducedsuccessively using the aforementioned steps. Since the step distance forincreasing and for reducing the switching threshold is identical, anychange that is made to increase or reduce the switching thresholdseveral times can also be reversed by making a corresponding number ofchanges in the opposite direction.

With a sensor having a single switching threshold that must be set, itis sufficient to have the two adjustment functions “increase switchingthreshold” and “reduce switching threshold.”

If several switching thresholds must be set in a sensor, a selection ofswitching thresholds to be adjusted can be provided as additionalfunctions to be set. For a sensor requiring the setting of two switchingthresholds, a third and fourth time window are provided in addition tothe first and second time window, which are assigned the function ofincreasing and/or reducing the switching thresholds. The third andfourth time windows follow the first and second time windows, preferablyin the direction of longer time periods.

To realize a switching threshold setting, the key must initially bedepressed for a longer period of time for selecting the switchingthreshold to be reset. This is followed by depressing the key for ashorter time to reset the switching threshold, wherein this threshold isrespectively increased or reduced, depending on whether the operation ofdepressing the key falls into the first or second time window.

The functionality of the parameter setting can be expanded by definingadditional time windows. If the length of time for activating the keyfalls into such an additional time window, then different parametersettings can be selected and changed. Examples of such additionalparameter settings are a light/dark switching operation for opticalsensors, as well as a setting for prolonging the pulse. This latterfunction results in prolonging the generated object detection signal forshort object interventions, meaning for sensor signals corresponding tothe detection of an object that is present only for a short period oftime. It means that if an object is detected only briefly, the objectreport generated by this detection is present for a longer time periodof time, so that it can be evaluated in a higher-ranking unit, such as acontrol unit.

The switching threshold setting according to the invention can be usedwith all different types of sensors, in particular with optical sensorsor ultrasonic sensors.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will be furtherunderstood from the following detailed description with reference to theaccompanying drawings, showing in:

FIG. 1 A schematic representation of an optical sensor according to theinvention; and

FIG. 2 A graph showing the representation of time windows specified inthe evaluation unit of the optical sensor according to FIG. 1.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates the configuration of an optical sensor1, operating on the basis of the light sensing principle. The opticalsensor 1 is provided with a sensing element, comprising a transmitter 3for emitting light rays 2 and a receiver 5 for receiving light rays 4,wherein the transmitter 3 can take the form of a light-emitting diode ora laser diode. In the simplest case, the receiver 5 is embodied asphoto-electric diode. The transmitter 3 and the receiver 5 are connectedto an evaluation unit 6 in the form of a micro-processor or the like.The evaluation unit 6 is used for activating the transmitter 3 and forevaluating the signals received at the receiver 5. The components of theoptical sensor 1 are installed inside a housing 7.

For object detection, the light rays 2 emitted by the transmitter 3 areconducted through a window that is not shown herein, thus arriving in anarea to be monitored. The light rays 2, which are reflected by an object8, are conducted as receiving light rays 4 through the window and to thereceiver 5.

In order to generate an object detection signal, the receiving signalsgenerated in this way and present at the receiver 5 are weighted withtwo switching thresholds. In the simplest case, amplitude values of thereceiving signals are weighted with the switching thresholds. For asensing element embodied as a distance sensor, distance values can beweighted with the switching thresholds as receiving signals for thereceiver 5.

The object detection signal obtained by weighting the receiving signalswith the switching thresholds generally indicates whether or not anobject 8 is located within a specified detection area, which forms apart of an area of coverage. The switching thresholds define the limitsof the detection area, thus forming so-called detection distances. Theobject detection signal is emitted via a switching output that is notshown herein.

A key 9 that can be activated by an operator is arranged on the outsideof the housing 7 for realizing the setting of the switching thresholdsor in general for adjusting parameters. A display element 10 in the formof a light-emitting diode is assigned to this key 9. The key 9 and thedisplay element 10 are connected to the evaluation unit 6 and arecontrolled by this unit. The display element 10 indicates to theoperator whether the depressing of the key has been recorded in theevaluation unit 6.

The key 9 makes it possible to generate and realize different settingfunctions by activating or depressing the key 9 for different periods oftime. The length of time for activating the key 9 is recorded andevaluated in the evaluation unit 6. Depending thereon, a specificsetting function is realized in the evaluation unit 6.

FIG. 2 illustrates this evaluation. The length of time recorded in theevaluation unit 6 for activating the key 9 is checked in order todetermine whether it falls into one of the time windows Z1-Z5, shown inFIG. 2. The time window Z1 is formed by the time interval 0<t≦0.2 s. Thetime window Z2 is formed by the time interval 0.2 s<t≦2 s. The timewindow Z3 is formed by the time interval 2 s<t≦7 s. The time window Z4is formed by the time interval 7 s<t≦12 s. The time window Z5 is formedby the time interval t>12 s.

The time windows Z2-Z4 are assigned setting functions in the evaluationunit 6 for setting the switching thresholds. Additional functions areassigned to the time window Z5, such as the light/dark switching of theoptical sensor 1 or the like.

The type of switching threshold to be set must be selected during aninitial step for realizing the setting of a switching threshold. If afirst switching threshold is to be selected, then the key 9 is depressedlong enough for the key activation to fall into the time window Z3. Ifthe activation interval recorded in the evaluation unit 6 falls into thetime window Z3, then the first switching threshold to be set isactivated by the evaluation unit 6. The same process is used foractivating the second switching threshold, wherein the length of timefor activating the key in that case must fall into the time window Z4.

Once the switching thresholds have been selected, their value is changedas a result of further activations of the key. If, in the process, thekey 9 is depressed once for a long enough interval so that the durationof the key activation falls into the first time window Z1, then thestarting value S₀ of the switching threshold is reduced by the amount ofΔS. On the other hand, if the duration of the key activation falls intothe time window Z2, then the starting value S₀ of the switchingthreshold is increased by the same amount of ΔS. The value of ΔS in thiscase amounts to less than 5% of the starting value S₀ of the switchingthreshold, which is specified in the evaluation unit 6. The amount ΔS,which represents the step value for resetting the switching thresholdeither to a positive or a negative value, is also stored in theevaluation unit 6.

If the switching threshold value is to be increased from the startingvalue S₀ to the value S₀+n·ΔS, then the key 9 must be depressed n times,each time long enough so that the duration of the key activation fallsinto the time window Z2.

The same is true for reducing the value of the switching threshold fromS₀−n·ΔS. In that case, the key must be activated n times so that eachtime the duration of the key activation falls into the time window Z2.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and that the same are intended to be comprehended withinthe meaning and range of equivalents of the appended claims.

1. A sensor comprising: a sensing element to generate output signalscorresponding to receiving signals received from an object; and anevaluation unit coupled to the sensing element and weighting the outputsignals from the sensing element with at least one switching thresholdto generate object detection signals, the evaluation unit including akey configured to selectively reset the at least one switching thresholdto higher and lower values through differences in activation of the key,wherein the differences in activation of the key are a function ofactivation time period of the key, wherein at least first and seconddifferent time windows are specified in the evaluation unit, and the atleast one switching threshold is reset to higher values if theactivation time period of the key falls into the first time window, andthe at least one switching threshold is reset to lower values if theactivation time period of the key falls into the second time window. 2.The sensor according to claim 1, wherein the key is adapted so that witha one-time activation of the key and an activation time period thatfalls into the first or second time window, the at least one switchingthreshold is respectively reset by the same amount.
 3. The sensoraccording to claim 1, wherein the first time window is defined by a timeinterval between 0.2s and 2s.
 4. The sensor according to claim 1,wherein the first time window has a lower limit that forms an upperlimit of the second time window.
 5. The sensor according to claim 4,wherein first and second switching thresholds are settable with the aidof the key.
 6. The sensor according to claim 5, wherein the key isadapted so that different periods of activation time are selectable toset the first or second switching threshold, respectively.
 7. The sensoraccording to claim 6, wherein a third and fourth time window isspecified in the evaluation unit, the first switching threshold to beset is selected if the activation time for the key falls within thethird time window, and the second switching threshold to be set isselected if the activation time for the key falls within the fourth timewindow.
 8. The sensor according to claim 7, wherein the third timewindow is defined by a time interval between 2s and 7s.
 9. The sensoraccording to claim 8, wherein the fourth time window is defined by atime interval between 7s and 12s.
 10. The sensor according to claim 9,wherein the sensor has additional functions that are settable byactivation time periods of the key that exceed the upper limit of thefourth time window.
 11. The sensor according to claims 1, furthercomprising a housing for the sensing element and the evaluation unit,wherein the key is arranged on an outside of the housing.
 12. The sensoraccording to claim 1, and further including a display element associatedwith the evaluation unit and the key to indicate whether an activationof the key was recorded in the evaluation unit.
 13. The sensor accordingto claim 12, wherein the display element comprises a light-emittingdiode.
 14. The sensor according to claim 1, wherein the sensor comprisesat least one of an optical sensor or an ultrasonic sensor.